For disperse dye manufacturers, with laboratory data comparing Jiefa ES series sodium lignosulfonate dispersants with Naphthalene (NNO), MF and 85A.
Conclusions • Tar is the hydrophobic synthesis by-product in every disperse dye press cake (P/C). It cannot be washed out, and at HTHP dyeing temperature it separates as free oil that produces dye specks, dye blotches and tar stains, worst of all in package dyeing and warp beam dyeing. • Three tests show tar before the dyeing house does: dispersibility at 71 °C, high-temperature dispersibility at 130 °C and a laboratory package dyeing test. Many manufacturers who rely on Naphthalene (NNO) do not run them. • Naphthalene (NNO) mills well and stains little, but it fails the 130 °C test (E/1), has a heat stability below 110 °C and carries about 20 % salt. The tar problem is not solved; it is passed to the dyeing house. • Jiefa ES series lignosulfonates hold tar inside dispersant micelles through 130 °C at a price comparable to Naphthalene (NNO). On a tar-containing press cake, package-dyeing pressure stayed at 0.23 bar with ES-7 versus more than 1.0 bar with 85A, dye residue grade 4–5 versus 1–2. |
What tar is, and what it does
Diazotization, coupling, condensation and after-treatment all leave by-products beside the target dye: unreacted intermediates, isomers, resinous condensation products and oxidation products. Dye chemists call the mixture tar. It is hydrophobic, amorphous and sticky, and it sits on the surface of the dye crystals in the press cake. How much a cake carries depends on the dye and synthesis route (chlorine-type Disperse Blue 79 is a well-known heavy carrier), on the intermediates and on the batch. Water washing does not remove a hydrophobic resin and recrystallization is too costly for commodity dyes, so tar goes straight into milling, spray drying and the dye bath.
In the dye plant it means longer and less predictable milling, free tar floating on the slurry, wall build-up in the spray-drying tower, and finished dyes that pass at release but coarsen, thicken or separate after hot storage.
In the dyeing house, as the bath heats toward 130 °C, tar separates from the dye particles as free oil. The droplets act as glue, collecting dye particles and polyester oligomers into a sticky mass that settles on the fabric as dye specks and dye blotches, or inside a yarn package as tar stains and an inner-to-outer shade difference; reduction clearing does little to it. Package dyeing and warp beam dyeing are hit hardest, because the wound yarn works as a depth filter at a low liquor ratio. Deep shades, sensitive dyes such as disperse turquoise blue, magenta and disperse violet, microfibers and polyester–spandex stretch fabric raise the risk further.
How to see tar before the dyeing house does
Dispersibility at 71 °C (AATCC 146). A heavily tar-loaded cake already fails here, with residue on the filter paper as the bath warms. Many dye specks are born at around 70 °C, not at 130 °C.
High-temperature dispersibility at 130 °C (GB/T 5541). A moderate tar load shows up here as residue, often a dark smeared ring rather than discrete particles.
Laboratory package dyeing with pressure logging. The most sensitive and most realistic test: polyester fibre packed on a perforated tube is dyed at 2.5–3 % with the bath pumped through it while the differential pressure is recorded. A cake that passes both filter-paper tests can still push the pressure past 1 bar.
The difficulty in many markets is not that these tests fail to show tar, but that they are not run. Where finished dyes are released on colour strength and particle size alone, tar leaves the dye plant unnoticed.
Why Naphthalene (NNO) seems to work, and what it hides
A dispersant’s classic job is electrostatic and steric stabilization of dye crystals. Tar is not a crystal. Holding it needs a second function: solubilization and emulsification of the tar into dispersant micelles that stay intact at 130 °C, which takes the right hydrophobic-to-hydrophilic balance, heat stability that survives HTHP dyeing, and low salt.
Naphthalene (NNO), a naphthalene sulfonate–formaldehyde condensate, is the default dispersant in many markets, and the manufacturers who use it are usually satisfied: it mills quickly, it is light in colour, it stains polyester very little, and it is cheap. The satisfaction comes from what is not being measured. Naphthalene (NNO) has a heat stability below 110 °C and carries roughly 20 % total salt, largely sodium sulfate; its small, rigid molecules give little steric protection, little capacity to solubilize tar, and desorb at HTHP dyeing temperature. In our laboratory two commercial samples both rated E/1 with heavy aggregation in the 130 °C test, a failing result for HTHP dyeing. Many manufacturers have never run the test.
Where much of the polyester is dyed as open, lightweight fabric such as saree material, specks and tar stains are far less visible than on a dense knit or a yarn package. The dye passes because the fabric forgives it. As soon as the same dye goes into package dyeing, warp beam dyeing, deep shades on dense fabric or export orders, the specks appear and the dyeing house carries the cost. The dye manufacturer has not solved the tar problem; it has handed it downstream. MF, the methylnaphthalene analogue, and general-purpose lignosulfonates such as 85A do better on heat stability and salt, but under package conditions they release tar too.
Indicator | Naphthalene (NNO), two commercial samples | MF | Jiefa ES series (ES-7) |
Chemistry | Naphthalene sulfonate–formaldehyde condensate | Methylnaphthalene sulfonate–formaldehyde condensate | Sodium lignosulfonate from natural softwood, ultrafiltered |
Total salt content | 20.61 % / 20.34 % | 4.89 % | 1.86 % |
Heat stability | < 110 °C | 130 °C | 155–160 °C |
High-temperature dispersibility (130 °C) | E/1, heavy aggregation | 23 s | Clean filter paper, 20–24 s |
Dispersibility at 71 °C | A/3 (AATCC class / residue grade) | 12 s | 12 s |
Reducibility | 0.15 % / 0.14 % | 3.02 % | 1.95 % |
Polyester staining by dispersant alone, ΔE (CIE) vs. undyed blank | 0.15 / 1.41 | 6.35 | 9.8–9.9 |
Table 1. Routine indicators measured in the Jiefa application laboratory under the same protocol (HG/T 3507, HG/T 3399, GB/T 5541-2017); dispersibility is reported as filtration time or as AATCC 146 class and residue grade depending on the test series. Naphthalene products stain less; none of the other indicators supports HTHP dyeing of tar-containing dyes.
How ES series sodium lignosulfonate dispersants control tar
The ES series are sodium lignosulfonates made from natural softwood lignin and purified by ultrafiltration. Their degree of sulfonation, molecular weight distribution and hydrophobic-to-hydrophilic ratio are set so that the dispersant adsorbs on the dye crystal and at the same time forms micelles that solubilize and emulsify tar. Free tar does not separate; it stays wrapped in the micelle and leaves the machine with the drain. Heat stability of 150–160 °C keeps that protection intact through HTHP dyeing, spray drying and hot container transport; low sulfate and low reducibility protect sensitive dyes in the oxygen-deficient, closed interior of a package.
For a manufacturer on Naphthalene (NNO), the change is a quality step, not a cost step: the ES series is priced in the same range, replaces Naphthalene (NNO) at a similar dosage in the same milling process, and moves the finished dye from a failing to a passing result in the 130 °C and package dyeing tests. ES-7 is the grade tuned for high-tar cakes and package dyeing; the data below were generated with it.
Laboratory results on tar-containing press cake
Cake: high-wash-fastness Blue GW:1, tar-containing; cake to dispersant 1:0.5; both dispersants milled to D90 < 1 µm under identical conditions; laboratory package dyeing at 2.5 % owf with the differential pressure logged throughout.
Test | ES-7 | 85A |
Milling time to D90 < 1 µm | 160 min | 170 min |
Heat stability (HG/T 3507) | 160 °C | 155 °C |
130 °C dispersibility, residue / filtration time (GB/T 5541) | 1.91 / 24 s | 3.41 / 30 s |
Package dyeing, max differential pressure | 0.23 bar, no peak | > 1.0 bar at 112.6 °C |
Package dyeing, dye residue grade | 4–5 | 1–2, heavy precipitation |
Polyester staining by dispersant alone, ΔE (CIE) vs. undyed blank | 9.88 | 11.95 |
Table 2. ES-7 versus 85A on a tar-containing Blue GW:1 press cake.
Figure 1. Package dyeing at 2.5 %. Both products reached the same particle size; the difference appears only under package conditions. With 85A the pressure rose from about 100 °C and the inner layers came out dark and oily; with ES-7 the pressure trace stayed flat and the package dyed level.
Storage stability at 70 °C (AATCC 146)
Disperse Blue 79, 250 % strength, cake to dispersant 1:0.55; the milled slurry was stored at 70 °C, roughly a shipping container in summer.
Storage at 70 °C | ES-7 | 85A |
Initial | 13 s, A/4 | 13 s, A/4 |
96 h | 13 s, A/4 | 14 s, A/3 |
144 h | 13 s, A/3 | 13 s, A/1, extensive aggregation |
Table 3. AATCC 146 results during hot storage of a 250 % Disperse Blue 79 slurry.
Figure 2. AATCC 146 filter papers, fresh and after 144 h at 70 °C.
FAQ
My Naphthalene (NNO) dyes get no complaints. Why change? Because the absence of complaints usually reflects the fabrics your customers dye, not the quality of the dye. Run the 130 °C test and a package dyeing test on your finished dye; if it fails, every customer who moves to packages, beams, dense fabrics or export inspection will find the problem before you do.
Where does Naphthalene (NNO) still fit? As a blend component for pale shades and pad dyeing, where its low colour and low staining help. As the main dispersant for HTHP dyeing of tar-containing dyes it fails on heat stability, 130 °C dispersibility and salt content.
Is any sodium lignosulfonate enough? No. Lignin source, purification, sulfonation and molecular weight distribution decide whether a lignosulfonate can hold tar at 130 °C, and on the same high-tar cake our own grades behave differently even when their routine indicators look alike: ES-7 is built for high-tar cakes and package dyeing, ES-3 is the general-purpose grade for standard cakes and pale shades. Test on your own cake under package conditions and let the result pick the grade.
Test the ES series on your own press cake
Tar comes from synthesis; whether it becomes a complaint is decided by the dispersant. Send us the cake you find hardest to standardize, or your current Naphthalene (NNO) finished dye. We will run it against the matching ES grade in the 71 °C, 130 °C, package dyeing and 70 °C storage tests and return a side-by-side report. Contact: [sales contact / email / WhatsApp to be inserted]
